Carbon nanotube film, carbon nanotube film precursor, method for manufacturing the same and a light source

ABSTRACT

A carbon nanotube film includes a plurality of successively oriented carbon nanotubes joined end-to-end by Van der Waals attractive force therebetween. The carbon nanotubes define a plurality of first areas and a plurality of second areas. The first areas and the second areas have different densities of carbon nanotubes. A method for manufacturing the same is also provided. A light source using the carbon nanotube film is also provided.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 200910106938.0, filed on Apr. 27, 2009 inthe China Intellectual Property Office.

BACKGROUND

1. Technical Field

The present disclosure relates to a carbon nanotube film, a carbonnanotube film precursor, a manufacturing method thereof and a lightsource including the carbon nanotube film.

2. Description of Related Art

Carbon nanotubes are tubules of carbon generally having a length of 5 to100 micrometers and a diameter of 5 to 100 nanometers. Carbon nanotubescan be composed of a number of co-axial cylinders of graphite sheets andhave recently attracted a great deal of attention for use in differentfields such as field emitters, gas storage and separation, chemicalsensors and high strength composites. However, it is very difficult tomanipulate the carbon nanotubes at a microscopic level. Thus, assemblingcarbon nanotubes into macroscopic structures is of great importance totheir applications at the macroscopic level.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments.

FIG. 1 is a schematic structural view of a carbon nanotube film of oneembodiment.

FIG. 2 shows a Scanning Electron Microscope (SEM) image of a carbonnanotube film of one embodiment.

FIG. 3 shows an SEM image of another carbon nanotube film of oneembodiment.

FIG. 4 is a schematic structural view of one embodiment of a carbonnanotube film precursor.

FIGS. 5A-5C illustrates successive stages of one embodiment of a methodfor manufacturing the carbon nanotube films of FIGS. 1-3.

FIG. 6 is a schematic structural view of a light source of oneembodiment.

FIG. 7 shows the relationship between degree of polarization and drawingangle for carbon nanotube films which are drawn out from carbon nanotubearrays with different heights.

FIG. 8 is a schematic structural view of a light source of oneembodiment.

FIG. 9 is a schematic structural view of a light source of anotherembodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to the embodiment shown in FIG. 1, a carbon nanotube film 20of one embodiment includes a plurality of successively oriented carbonnanotubes joined end-to-end by Van der Waals attractive force. Thecarbon nanotubes in the carbon nanotube film 20 can be substantiallyaligned in a first direction D1, as shown in FIG. 1.

The carbon nanotube film 20 can be divided into a plurality of firstareas 204 and a plurality of second areas 205 according to densities ofcarbon nanotubes. The first areas 204 and the second areas 205 havedifferent densities of carbon nanotubes. For example, as shown in FIG.1, the first areas 204 have a density of carbon nanotubes larger thanthat of the second areas 205. The first areas 204 and the second areas205 are alternately arrange along the first direction D1. In each of thefirst areas 204 and the second areas 205, the carbon nanotubes canuniformly distribute along a second direction D2, as shown in FIG. 1.The second direction D2 can be perpendicular to the first direction D1.Referring to FIGS. 2-3, each of the first areas 204 and the second areas205 has an approximately successive wave shape. The carbon nanotube filmshown in FIG. 2 is drawn out from a carbon nanotube array with a heightof about 400 microns, and the carbon nanotube film shown in FIG. 3 isdrawn out from a carbon nanotube array with a height of about 600microns. The carbon nanotube films of FIGS. 2-3 are drawn out at adrawing angle of about 65 degrees according to a method of oneembodiment, which will be described in the following text.

Referring to the embodiment shown in FIG. 4, a method for manufacturingthe carbon nanotube film 20 includes the steps of:

Step (1): providing a carbon nanotube array 50 and a drawing tool 30,the carbon nanotube array 50 including a plurality of carbon nanotubes56 arranged on a substrate 52 approximately along a growth direction D3of the carbon nanotubes 56, as shown in FIG. 4;

Step (2): positioning the drawing tool 30 close to the carbon nanotubearray 50 and selecting some carbon nanotubes 56 of the carbon nanotubearray 50;

Step (3): drawing the selected carbon nanotubes 56 away from the carbonnanotube array 50 along a drawing direction D4 shown in FIG. 4 tofabricate the carbon nanotube film 20, an acute angle α of inclinationbetween the drawing direction D4 and the growth direction D3 being lessthan or equal to 80 degrees. The acute angle α is also referred to asdrawing angle α.

In step (1), the carbon nanotube array 50 can be manufactured using achemical vapor deposition method, a plasma vapor deposition method or anarc discharge method. In one embodiment, the carbon nanotube array 50 ismanufactured using a chemical vapor deposition method, and this methodincludes the steps of:

Step (a): providing the substrate 52. The substrate 52 can be a p-typeor n-type silicon wafer, or a silicon wafer with a film of silicondioxide thereon. A smoothness of a surface of the substrate 52 is lessthan 1 micron for facilitating a uniform formation of a catalyst layerdirectly on the surface of the substrate 52.

Step (b): depositing a catalyst on the substrate 52 to form a catalystlayer 54. The catalyst can be iron, cobalt, nickel or alloys of thesame. The catalyst layer 54 has a thickness in the range of aboutseveral nanometers to about several hundred nanometers.

Step (c): annealing the substrate 52 with the catalyst layer 54 in airat about 300 to about 400° C. for about 5 to about 15 hours, therebyoxidizing the catalyst layer 54 to form nano-sized catalyst oxideparticles.

Step (d): putting the substrate 52 with the nano-sized catalyst oxideparticles into a furnace (not shown) and heating the furnace up to apredetermined temperature with flowing protective gas. The protectivegas can be noble gas or nitrogen. In the preferred method, argon is usedas the protective gas. The predetermined temperature varies according tothe catalyst used. In the preferred method, iron is a catalyst, and thepredetermined temperature is about 500 to about 700° C.

Step (e): introducing a mixture of a carbon source gas and a carrier gasinto the furnace, thus forming the carbon nanotubes 56 extending fromthe substrate 52 along a growth direction D3 as shown in FIG. 4. Thecarbon source gas can be acetylene, ethylene, or another suitablechemical compound which contains carbon. The carrier gas can be a noblegas or nitrogen. A flow rate of the carbon source gas is about 20 toabout 50 standard cubic centimeters per minute. A flow rate of thecarrier gas is about 200 to about 500 standard cubic centimeters perminute. Thus, the carbon nanotube array 50 of step (1) is formed.

In step (2), the drawing tool 30 can be an adhesive tape, tweezers, oranother tool allowing multiple carbon nanotubes to be gripped and pulledsimultaneously. In one embodiment, adhesive tape with a predeterminedwidth applies as a drawing tool 30 to contact and select some carbonnanotubes 56 of the carbon nanotube array 50. The selected carbonnanotubes 56 are also referred as carbon nanotube bundles. A carbonnanotube bundle is any plurality of carbon nanotubes formed in acontiguously adjacent group in the carbon nanotube array 50.

In step (3), selected or initial carbon nanotube bundles, which areattached to the drawing tool 30, are first drawn out from the carbonnanotube array 50 along the drawing direction D4 shown in FIG. 4 tofabricate the carbon nanotube film 20. During the drawing process orpulling process, as the initial carbon nanotube bundles are drawn out,other carbon nanotube bundles are also drawn out end to end due to theVan der Waals attractive force between ends of adjacent bundles. Then,the carbon nanotube film 20 is fabricated.

In step (3), when the carbon nanotube film 20 is not cut off from thecarbon nanotube array 50 and there are still some carbon nanotubes 56existing on the substrate 52, the carbon nanotube film 20 and theremaining carbon nanotube array 50 form a carbon nanotube filmprecursor. The carbon nanotube film precursor includes the substrate 52,some remaining carbon nanotubes 56 on the substrate 52, and the carbonnanotube film 20 connected to the remaining carbon nanotubes 56.

Furthermore, the drawing process of step (3) can be further divided intoseveral successive stages, as shown in FGS. 5A-5C. These successivestages include:

(I) As shown in FIG. 5A, the drawing tool 30 is applied to contact a topend edge of the carbon nanotube array 50 to select a plurality of firstcarbon nanotube bundles 201.

(II) As shown in FIG. 5B, top ends of the first carbon nanotube bundles201 are first separated from the carbon nanotubes 56 when the drawingtool 30 is moved. Then, bottom ends of the first carbon nanotube bundles201 are separated from the substrate 52.

(III) When the bottom ends of the first carbon nanotube bundles 201 aremoving away from the substrate 52, the bottom ends of the first carbonnanotube bundles 201 begin to draw bottom ends of adjacent second carbonnanotube bundles 202 due to the Van der Waals attractive forcetherebetween.

(IV) The bottom ends of the second carbon nanotube bundles 202 are firstseparated from the substrate 52 before top ends of the second carbonnanotube bundles 202 are separated from the substrate 52. As shown inFIG. 5C, the first carbon nanotube bundles 201 and the second carbonnanotube bundles 202 are separated from the substrate 52.

(V) As the top ends of the second carbon nanotube bundles 202 are movingaway from the substrate 52, the top ends of the second carbon nanotubebundles 202 begin to draw top ends of adjacent third carbon nanotubebundles 203 due to the Van der Waals attractive force therebetween.

Repeating stage (II), stage (III), stage (IV) and stage (V), the carbonnanotube film 20 can be formed. Further, in different stages, thedrawing tool 30 can move different distances in the drawing directionD4. For example, the height of the carbon nanotubes 56 is supposed to beL. In stage (II), as shown in FIG. 5B, a distance Δd that the drawingtool 30 moves in the drawing direction D4 is L(1+cos α). While in stage(IV), a distance Δd′ that the drawing tool 30 moves in the drawingdirection D4 is L(1+cos α). A difference in value between the distanceΔd and the distance Δd′ is 2L cos α. Since the carbon nanotube film 20is fabricated at a uniform speed, the first carbon nanotube bundles 201of the stage (II) are separated from the carbon nanotube array 50 at aslower rate than the second carbon nanotube bundles 202 of stage (IV).In other words, the first carbon nanotube bundles 201 are separated fromthe carbon nanotube array 50 at a first rate and the second carbonnanotube bundles 202 are separated from the carbon nanotube array 50 ata second rate, which is larger than the first rate. The rate differencecan result in the distribution of densities of carbon nanotubes of thecarbon nanotube film 20 as described above. The first areas 204 are theresults of stage (II) and stage (III). The second areas 205 are theresults of stage (IV) and stage (V), and thus, have a density smallerthan that of the first areas 204.

The carbon nanotube film 20 and the method for manufacturing the samehave been described above. Some examples of using the carbon nanotubefilm 20 are described below.

Referring to the embodiment shown in FIG. 6, a light source 70 of oneembodiment includes a carbon nanotube film 20 and two electrodes 72. Thetwo electrodes 72 electrically connect to the carbon nanotube film 20.The two electrodes 72 are disposed on opposite ends of the carbonnanotube film 20.

When an electrical current flows through the carbon nanotube film 20 viathe two electrodes 72, the carbon nanotube film 20 can emit polarizedlight. The polarization direction of the polarized light can be parallelto the axial direction of the carbon nanotubes of the carbon nanotubefilm 20, because the carbon nanotubes are one-dimensional material andelectrons have restricted movement along the axial direction of thecarbon nanotubes.

The relationship between degree of polarization and drawing angle forcarbon nanotube films are illustrated in FIG. 7. The curve A1 in theFIG. 7 represents a carbon nanotube film which is drawn out from acarbon nanotube array having a height of about 235 microns. The curve A2in the FIG. 7 represents a carbon nanotube film which is drawn out froma carbon nanotube array having a height of about 410 microns. The curveA3 in the FIG. 7 represents a carbon nanotube film which is drawn outfrom a carbon nanotube array having a height of about 608 microns. Asshown in FIG. 7, the larger the drawing angle, the larger the degree ofpolarization of emitted polarized light. The higher the carbon nanotubearray, the larger the degree of polarization of emitted polarized light.

Further, in the carbon nanotube film 20, the first areas 204 and thesecond areas 205 have different densities of carbon nanotubes, resultingin the first areas 204 and the second areas 205 having differentresistances. Thus, when an electrical current flows through the carbonnanotube film 20, the first areas 204 and the second areas 205 will havedifferent luminous intensities. In other words, the carbon nanotube film20 can produce alternately dark and bright wave shaped bands.

Referring to the embodiment shown in FIG. 8, a light source 80 of oneembodiment includes the carbon nanotube film 20, the two electrodes 72and a support 82. The carbon nanotube film 20 is supported on thesupport 82. The support 82 can be transparent or translucent.

Referring to the embodiment shown in FIG. 9, a light source 90 ofanother embodiment includes the carbon nanotube film 20, the twoelectrodes 72, a first frame 92 and a second frame 94. The carbonnanotube film 20 is sandwiched between the first frame 92 and the secondframe 94.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the disclosure. Variations maybe made to the embodiments without departing from the spirit of thedisclosure as claimed. Elements associated with any of the aboveembodiments are envisioned to be associated with any other embodiments.The above-described embodiments illustrate the scope of the disclosurebut do not restrict the scope of the disclosure.

1. A carbon nanotube film comprising: a plurality of first areas and aplurality of second areas, the first areas and the second areas eachcomprising a plurality of successively oriented carbon nanotubes joinedend-to-end by Van der Waals attractive force therebetween, wherein thefirst areas and the second areas have different densities of carbonnanotubes.
 2. The carbon nanotube film of claim 1, wherein the firstareas and the second areas are alternately arranged along a firstdirection.
 3. The carbon nanotube film of claim 2, wherein the firstdirection is approximately parallel to an axial direction of the carbonnanotubes.
 4. The carbon nanotube film of claim 2, wherein carbonnanotubes of each of the first areas and the second areas, areapproximately uniformly distributed along a second directionapproximately perpendicular to the first direction.
 5. The carbonnanotube film of claim 4, wherein the carbon nanotubes of each of thefirst areas and the second areas, are approximately parallel to oneanother.
 6. The carbon nanotube film of claim 1, wherein each of thefirst areas and the second areas has a successive wave shape.
 7. A lightsource comprising: a carbon nanotube film comprising a plurality offirst areas and a plurality of second areas, the first areas and thesecond areas each comprising a plurality of successively oriented carbonnanotubes joined end-to-end by Van der Waals attractive forcetherebetween, wherein the first areas and the second areas havedifferent densities of carbon nanotubes; and two electrodes electricallyconnected to the carbon nanotube film.
 8. The light source of claim 7,further comprising a support supporting the carbon nanotube film.
 9. Thelight source of claim 7, wherein the support is transparent ortranslucent.
 10. The light source of claim 7, further comprising a firstframe and a second frame, wherein the carbon nanotube film is sandwichedbetween the first frame and the second frame.
 11. The light source ofclaim 7, wherein the first areas and the second areas are alternatelyarranged along a first direction, and the first direction isapproximately parallel to an axial direction of the carbon nanotubes.12. The light source of claim 11, wherein the two electrodes aredisposed on opposite ends of the carbon nanotube film along the firstdirection.
 13. The light source of claim 11, wherein carbon nanotubes ofeach of the first areas and the second areas, are approximatelyuniformly distributed along a second direction approximatelyperpendicular to the first direction.
 14. The light source of claim 11,wherein carbon nanotubes of each of the first areas and the secondareas, are parallel to one another.
 15. The light source of claim 11,wherein each of the first areas and the second areas has a successivewave shape.
 16. A method for manufacturing a carbon nanotube film, themethod comprising the steps of: Step (1): providing a carbon nanotubearray and a drawing tool, the carbon nanotube array comprising aplurality of carbon nanotubes arranged on a substrate approximatelyalong a growth direction of the carbon nanotubes; Step (2): positioningthe drawing tool close to the carbon nanotube array and selecting somecarbon nanotubes of the carbon nanotube array; Step (3): drawing theselected carbon nanotubes away from the carbon nanotube array along adrawing direction at a drawing angle, the drawing angle being an angleof inclination between the drawing direction and the growth direction,the angle being less than or equal to 80 degrees, thereby forming thecarbon nanotube film, wherein the carbon nanotube film comprises aplurality of first areas and a plurality of second areas, the first andsecond areas each comprising a plurality of successively oriented carbonnanotubes joined end-to-end by Van der Waals attractive forcetherebetween, the first areas and the second areas having differentdensities of carbon nanotubes.
 17. The method of claim 16, wherein thedrawing angle is about 65 degrees.
 18. The method of claim 16, whereinthe drawing angle is about 35 degrees.
 19. The method of claim 16,wherein the substrate has a flat surface and the growing direction isapproximately perpendicular to the surface of the substrate.